The aim of this study was to investigate aerobic biodegradability of phenol, resorcinol and 5-methylresorcinol and their different two-component mixtures using activated sludge sampled from the Kohtla-Järve wastewater treatment plant. The degradation behaviour of phenolic compounds was investigated by respirometry. Non-linear regression analysis was used for determination of the kinetic parameters such as the maximum rate of oxygen uptake (max , O 2 V), the maximum rate of substrate bio-oxidation (V max) and the half-saturation coefficient (K S). Various kinetic models were tested to obtain the best curve fit. It was shown that the activated sludge degraded resorcinol and 5-methylresorcinol more slowly than phenol. Among the studied substrates phenol had the highest values of max , O 2 V , V max as well as the ratio of max , O 2 V /K S. Activated sludge had the highest affinity to phenol with the lowest K S value. Among all studied bi-substrate systems the highest max , O 2 V values were found for phenol (0.1 mM)-5-methylresorcinol. As the kinetic parameters and short-term oxygen demands are functions of the compound undergoing biodegradation and the composition of the microbial community performing the degradation, therefore the results of this study have importance in explanation of effectiveness of wastewater treatment process and of the influence of polluting compounds on it.
The aim of this study was to investigate the biodegradation of phenol, o-cresol and p-cresol individually and as bi-substrate mixtures at low initial substrate concentrations. Activated sludge was taken from the Kohtla-Järve wastewater treatment plant, Estonia, which is also treating phenolic wastewater from the oil-shale chemical industry and is considered to be acclimated to the phenolic compounds. Respirometric data have been used for evaluation of the kinetic parameters describing the bio-oxidation of substrates. Activated sludge was able to degrade phenol and p-cresol faster than o-cresol, showing better affinity to p-cresol. However, at higher concentrations, phenol and p-cresol exhibited also an inhibitory effect to the microorganisms. The highest values for maximum rate of oxygen uptake (V(O2,max)) were obtained for the bi-substrate system of phenol--p-cresol among the mixtures containing both substrates at equal concentrations from 0.005 mM to 0.050 mM. Concerning the systems containing one substrate at 0.1 mM and the other substrate varied in the abovementioned range, the highest V(O2,max) values were found for phenol--o-cresol(0.1 mM). The interaction parameters indicated that phenol had a stronger inhibition effect on the biodegradation of p-cresol than p-cresol had on the biodegradation of phenol. However, the obtained interaction parameters for systems of phenol--o-cresol indicated that o-cresol had a stronger inhibition effect on the biodegradation of phenol, which in turn had a mild inhibition or even enhancing effect on the biodegradation of o-cresol. In the case of a 1:1 mixture, phenol and o-cresol had a similar mild inhibition effect on each other's biodegradation.
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